1. Field of the Invention
The present invention relates to a hydraulic circuit for an option tool of heavy equipment which is capable of selectively engaging an option tool (referred to breaker, share, etc.) to a work apparatus such as a boom, etc., and in particular to a hydraulic circuit for an option tool of heavy equipment implemented in such a manner that hydraulic fluid is efficiently supplied by a necessarily set amount during a combined work in which a work apparatus and an option tool are concurrently operated by engaging an option tool having different operation pressures at an end portion of a work apparatus.
2. Description of the Background Art
Generally, in a construction heavy equipment such as an excavator, etc., a breaker having a relatively lower operation pressure or an option tool such as a share, etc. having a relatively higher operation pressure is selectively engaged by disassembling a bucket in order to maximize a work condition or work efficiency. Here, a work apparatus spool or option tool spool is installed in a main control valve in order to control hydraulic fluid supplied to a work apparatus such as a bucket or an option tool.
Among the terminologies used herein, the terminology “Negative system” represents a method for decreasing a discharge amount of a variable displacement hydraulic pump in the case that pilot pressure discharged from an upper stream of a pilot signal generation unit installed in a down stream of a center bypass path is high and increasing a discharge amount of a hydraulic pump in the case that the pilot signal pressure is low.
In addition, the terminology “Positive system” represents a method for increasing a discharge amount of a variable displacement hydraulic pump in the case that pilot pressure applied to a directional switching valve adapted to control hydraulic fluid supplied to a hydraulic cylinder is high and decreasing a discharge amount of a hydraulic pump in the case that pilot pressure is low.
As shown in FIG. 1, a hydraulic circuit for an option tool of heavy equipment in a conventional art includes a variable displacement hydraulic pump 2 and a pilot pump 3 which are connected with an engine 1 and are driven, a work apparatus (not shown) and an option tool 4 which are connected with the variable displacement hydraulic pump 2 and are driven when hydraulic fluid is supplied, a main control valve 6 which is installed in a flow path between the hydraulic pump 2 and the work apparatus, and the hydraulic pump 2 and the option tool 4 and is formed of an option tool spool 5 and a work apparatus spool for controlling a start, stop and direction change of the work apparatus and option tool 4, and a first electromagnetic proportion valve 8 which is installed in a flow path between the pilot pump 3 and the hydraulic pump 2 and outputs a secondary pressure corresponding to an electric signal from a controller 7 for thereby variably controlling a discharge amount of the hydraulic pump 2.
In the drawings, reference numeral 9 represents a remote control valve (RCV) adapted to control pilot pressure switching a corresponding spool of the main control valve 6. 10 represents an option flow amount adjusting apparatus for inputting a signal into a controller 7, wherein the signal corresponds to a set flow amount needed in the option tool 4 for controlling hydraulic fluid supplied to the option tool.
Therefore, when a breaker having a relatively lower operation pressure or a share having a relatively higher operation pressure than that of a breaker and operating under a high pressure work condition is engaged to a work apparatus as an option tool 4, pilot pressure from the pilot pump 3 is applied to the option tool spool 5 based on an operation of the remote control valve 9. As shown in FIG. 1, the pilot signal pressure is switched in a left or right direction and passes through the option tool spool 5, so that an operation pressure from the variable hydraulic pump 2 is switched. The pilot signal pressure is supplied to the option tool 4 for thereby performing a desired work.
A certain signal corresponding to the set flow amount is inputted into the controller 7 through an additionally provided option flow amount adjusting apparatus 11, so that a set flow amount needed in the option tool 4 is supplied. A certain current value corresponding to an input signal is inputted into a first electromagnetic proportion valve 8 in accordance with a control of the controller 7.
As shown in FIG. 3, in the above first electromagnetic proportion valve 8, a signal pressure (referred to a secondary pressure passing through the port A) from the pilot pump 3 to correspond to the current value is outputted to a discharge amount controller of the variable displacement hydraulic pump 2, so that the maximum discharge amount of the hydraulic pump 2 is limited. Therefore, it is possible to discharge a desired amount of hydraulic fluid needed in the option tool 4.
However, in the conventional option tool hydraulic circuit, in the case that a combined work is performed in such a manner that the option tool is operated concurrently with a boom, arm, rotation device, etc., the maximum discharge amount of the variable displacement hydraulic pump 2 is limited (referred to a negative flow amount control method indicated by the curve “a” in FIG. 2). In this case, an operation speed of the work apparatus is decreased, and a combined operation is not properly performed. Therefore, workability is decreased. The work apparatus or option toll 4 may not properly operate, so that a safety accident may occur. There may be a big problem in the safety.
In the case that a hydraulic system which is designed to discharge a maximum flow from the variable displacement hydraulic pump 2 (referred to a positive flow amount control method indicated by the curve “b”), when a work apparatus such as a rotation apparatus, etc. and an option tool 4 are concurrently operated, a certain flow amount of hydraulic fluid is supplied more than the set flow amount needed in the option tool 4 due to a load pressure difference between the option tool 4 and the work apparatus. Therefore, the option tool 4 may be damaged, and durability is decreased. The optical tool may be exchanged.